decreasing compression ratio in 3B (1 Viewer)

[magnus_heydoc]

turbo 3B

Someone here mentioned the possibility that a turbo 3B has a tendency to spin more bearings.

I've got 2 turbo 3B's. One has been turbo by the PO for around 10 years, has perfect oil pressure according to the 60 series gauge, it's last compression test numbers were 410,418,412,420 and it's got around 400k kms on it. It runs 9-10lbs of boost on a garett turbo from a volvo 240. EGT's never exceed 550 C.

My other 3B I turbo'ed 3 years ago. It has around 60k kms since a full rebuild, it runs 14lbs of boost on a Mitsu turbo from a Volvo 740. It runs between 200-400 kpa for pressure on a quality pressure gauge. (No compression test numbers for this one). EGt's never exceed 500 C.

My point is that a turbo does not seem to wear out your 3B as long as you don't get it really hot temp. wise or EGT wise and you don't run crazy boost. (I feel anything 15lbs or less is reasonable and conservative). The compression ratio difference may not be bothering anything. There seems to be lots of turbo 3Bs on this site that run a long time without problems.

If your EDIC is shutting your motor down b/c of low oil pressure it may be just doing it's job protecting your motor. You may for some reason have periods of low pressure that the EDIC is responding to and it may not be relays or sensors. Maybe the bottom end was just worn out?
FWIW,
Aaron

 

[slammed41]

aaron,

thanks for the input. i'm glad to read you've had long term success with a turbo'd 3B. that's good news!

as is often the case, this story has been twisted beyond its original intent. i never stated that, in general, turbo'd 3Bs have a tendency to spin bearings...just that my turbo'd 3B did spin a bearing. me thinks that some folks are reading between the lines or not reading at all!

here's the deal: i had a bearing spin on a turbo'd 3B. prior to the incident, the engine ran fine. the turbo was installed by the PO, and i did not have any real history of the engine's life and condition prior to purchasing the vehicle. the odometer failed at some point, so the total miles/kms was unknown but likely high (over 400K). the turbo was wastegated at 15 psi.

so, after the spun bearing incident, i was thinking of ways to increase the longevity of the next engine. knowing that 13B-T engines run at lower boost pressures and a lower compression ratio, i thought that perhaps the higher boost and compression ratio that i was running may have contributed to engine failure. i'm not a mechanic...just grasping at ideas.

as you may have read in the replies to this post, other folks believe the bearing failure was caused by reasons other than high boost pressures or high compression ratios. if so, that's great news! know that i know i was barking up the wrong tree, i'm happy to find more appropriate trees to bark up!

what i want is to be able to keep my present power levels while maintaining a higher level of longevity. in other words, i'd like to keep running 15 psi, keep the fuel screw turned out a few threads AND keep the engine together without costing an arm and a leg.

i'm not trying to build a race engine and i can't afford to build an engine from scratch. as wayne mentioned earlier, by cleaning the oil galleries and installing new BEBs in my donor engine, i can probably add a few years of life to it. i'm also considering an external oil cooler and an intercooler to reduce overall heat buildup. my radiator could probably use a rebuild, too. oh, i will likely install an aftermarket oil pressure gauge...i've never been a fan of factory gauges.

any other tidbits or ideas regarding engine longevity while maintaining reasonable power and budget levels are welcome!

cheers,

r

 

[crushers]

do as suggested
and
at the same time install an aftermarket oil pressure gauge, a pyrometer and an boost gauges. factory units are just glorified idiot lights.
you can boost it to what ever you wish but VERY seldom will you ever see full boost and if you do you will be pushing the old girl hard either bucking a head wind, climbing a hill (steep or long and gentle) or towing. normally the boost will be at ABOUT 6 psi on the highway.

you asked a common question and made a common assumption.

 

[baxter650]

For what it's worth you could talk to a cam grinder, back in the muscle car days manufacturers used the cam to bleed off excess compression.
They did this by decreasing lobe separation angle that was ground into the camshaft, increasing valve overlap.
I am not sure you could gain much through a regrind, but you could ask.
On the subject of milling pistons, does the 3B utilize a "quench area"?
The reason i ask is that the quench area in most engines is used to create turbulence increasing fuel atomization and a more even burn.
Milling the entire top of the piston would reduce or even negate this turbulence.
Milling an area mirroring the combustion chamber shape or as in a Chevy piston, a ''D" shape into the piston may be the better way to go.
How much of this translates over to diesel i don't know but all fuel engines are just glorified air pumps, so they should be subject to the same physics.

 

[gerg]

The 3Bs have a flat top piston with no obvious squish area. There are recesses cut for the valves as well as a narrow dish for the pre cup fuel stream. I was planning on taking 1 or 2mm off the top, having the valve recesses re-cut but leave the dish alone as it would be quite expansive to reproduce. This would alter the fuel stream somewhat, but to what extent I am not sure.
g

 

[baxter650]

If there is a quench area it would be the flat portion of the head over the piston.
The portion shaded in blue.
I can't see flycutting the valve reliefs them selves deeper , i would probably take my 1mm or more, (depending on crown thickness) off that side of the piston leaving the trough be.
How many points of compression are you looking to loose by milling the pistons?
I guess all i am saying is there is more to loosing compression than whacking material off a piston
For an example, if you add a thicker or a second head gasket to a small Chevy to lower compression because of detonation you run the very real risk of worsening the problem by reducing turbulence from in the quench area.
Again i know this is a diesel so it may not apply, but then again.

 

[gerg]

Not to hijack this guys thread but my situation is somewhat different as I am taking the piston down to accommodate thicker ceramic coatings and would most likely get the majority of the CR drop from de-shrouding the valves and cutting the valves themselves. I was looking for around a 2 point drop. I haven't screwed around with my test head to see how much I need to remove to accomplish that. I really dont want to take too much out as to lower the VE.
g

 

[baxter650]

I wouldn't say you/we are hijacking, this is one of the very points he wanted opinions on.
I would guess that two points would be about 20-30 CCs of material.
If it was me doing it i would spread it around and unshroud the valves as well as milling some off the pistons.
A cam could be interesting to play with too, i have already given it some thought and have a core waiting.
Lowering compression was not the intent, but if i do have one ground that is a question i will ask.

 

[gerg]

Well I am going to change out my rad for a 4 core and plan to do the cam at that time. The guy who ground my cam emphasized the exhaust lobe for me. He is a really down to earth and does quality work. He is unfortunately waiting for me to report back some numbers to him for changes to be implemented for future profiles. He has been waiting a while, doh. Here is his site.
Colt Cams - custom camshaft grinding


On the topic of de-shrouding the valves, how much is too much? Vs lift and valve diameter? All that stuff is fairly closely guarded info. Sucks.
g

 

[baxter650]

With a head that is prone to cracking i would be very timid with a cutter.
The trough i would avoid like the plague, i would limit unshrouding to a few mm and break off the sharp edge to a nice radius.
I think there are more gains to be made in the bowls, particularly where the valve seats transition into the bowls.
I spent most of my time cleaning up these areas as there was quite a lip left between the port and the bottom of the seat.
The rest of the port i just took off the large lumps then smoothed them out removing very little material.

 

[gerg]

Nice. I have taken comfort that the 3B heads have so much casting and s***e in the runners that there is alot of room for improvement. The bowls are just hideous for valve seat transitions. I think my lawnmower has a smother flowing head. Sadly I was joking , but after thinking about it, its probably true.

I noticed that you left the boss alone and I might be wrong, but those valves dont look to be deshrouded more than stock. Some folks I see do all sorts of stuff to the bosses. I was thinking of slimming their profile a tad, but leave the majority of it there for valve support, especially on the exhaust side. Ive seen some jobs where guys just hog the whole thing off. Somehow I don't think that's a great idea.

Did you do anything to the short side of the runner? When I feel there it is quite abrupt and angular.
Looks good.
g

 

[crushers]

now, i am curious, i know that for high reving gassers there is a benefit to porting and polishing
but
on a low reving diesel what really is the benefit?

it seems all the Toyota 1HZ/PZ/KZ/L/B/H series heads have "cracking between the valves" issues to some degree, wouldn't taking meat off the walls be a bit detrimental to an already proven issue?

hummm...

 

[baxter650]

gerg, you are correct, i have not touched the bosses or deshrouded the valves.
crushers, not having access to a flow bench i can't be certain but judging by what i have read it will help low lift flow (again small chevy stuff) low lift #s are usually low velocity.
And this is now force fed so it certainly can't hurt.
Any sharp edge is a stress riser and more prone to develop a crack.
I also later had the exhaust ports ceramic coated.

 

[crushers]

humm, even force fed it still revs max at 4100 unless you changed the max rpm screw.

not knocking what you are doing, just trying to understand.

as for sharp edges that is interesting, i will have to do more research on that point.

thanks

 

[Dougal]

Regardless of rpm, there are advances to be made in cylinder fill which will mean more torque and power and quicker turbo spool.

The question that remains is how big can the gains be on this engine? 5%, 10%?

 

[baxter650]

Indeed that is the question, the answer i think would lie somewhere beyond the pile of destroyed engines, sacrificed only to find the next weakest link.
I will mess with the 3B a bit using what has been proven to work on other engines, but i do not expect huge gains.
The real question is, can you live with the limited power the 3B makes.

 

[crushers]

and the answer is:
if you can't you swap engines
or
change the demand put upon the engine

 

[gerg]

I guess the way I look at it is that it is inefficient and irritates the crap out of me. I would be quite Happy with 5% VE gain. I doubt that one mod by itself will net tremendous gains, but combine several of them together and it can really add up.

I also am sick of my wife complaining about how slow my freakin truck is compared to my friends cummins when we go RVing. Before working on my motor being passed by loaded semi trucks up hill was a constant threat!

In my family my truck has to do everything. Haul the RV... fast, get groceries and park in tiny parking spots, pack the whole family around, go 4x4ing, actually be drivable by my tiny wife and above all get great mileage for commuting. Its tuff to do all these things well, but eventually my truck will.
g

 

[Dougal]

Next you should find an injection pump off an Isuzu 4BD2 and see if you can swap plungers across.
From this site someone posted up a pump number stating the 3B engines had 7mm plungers, the Isuzus have either 9, 9.5 or 10mm plungers and they're the same basic type of pump.

9mm plungers with the same stroke will give 30% more fuel than 7mm plungers.

Or maybe just shoe-horn in a a 4BD1T when she's not looking and strap your compound turbos to it. Will give about 200hp and 600Nm depending on the pump.

 

[gerg]

Yes the Isuzu would have been a great choice but I already have too much time and money invested in my 3B to start over again. Plus my wife has actually learned over time what stuff is so just saying "im going to work on the truck" doesn't work anymore. I swear she has a list and keeps track of all the projects I do.

I was going to re do the pump in the future so that plunger option is very tempting indeed. Are old pumps common for those Dougal or can you just get the plungers by themselves?
g